It is well known that any significant reduction or restriction in the flow of blood through the arteries of the body can cause complications which may have serious consequences. In any event, it is extremely important for the health of the patient that a stenosis, or blockage, which is causing such a condition be eliminated. One well known and frequently used procedure to accomplish this task is popularly known as angioplasty. For a basic angioplasty procedure, a dilatation balloon is positioned in the arterial lumen at the stenosis and the balloon is inflated to open the artery by dilating the plaque-restricted lumen at the stenosis. The plaque, however, remains in the artery and is not removed. Unfortunately, in some cases, it appears that the plaque which is left behind in the artery may cause another stenosis to form.
As an alternative to angioplasty, atherectomy procedures have been developed to resolve the problems caused by blocked arteries. However, unlike an angioplasty procedure which only dilates the lumen at the stenosis but does not remove the plaque from the artery which caused the stenosis, in accordance with an atherectomy procedure the plaque which is creating the stenosis is mechanically cut from the artery and then removed. The cutting devices which are used for this task must, of necessity, be rather small. On the other hand they must have sufficient structural strength to cut the plaque in performance of the atherectomy procedure. Additionally, they must be operationally reliable. Many examples of such cutting devices can be given. For instance, U.S. Pat. No. 4,895,166 which issued to Farr et al. for an invention entitled "Rotatable Cutter for the Lumen of a Blood Vessel", and which is assigned to the same assignee as the present invention, discloses such a cutter. U.S. Pat. No. 4,589,412 which issued to Kensey for an invention entitled "Method and Apparatus for Surgically Removing Remote Deposits" is but another example.
One problem which must be confronted in any procedure, whether it be an angioplasty or an atherectomy procedure, is the size of the entry site which can be used for introducing the medical device being used into the artery. Standard practices accept an entry site which has a diameter of only approximately twelve French, i.e. about four millimeters. Thus, any device which is to be positioned in the artery must pass through an introducer whose outer diameter is not larger than twelve French. The inner diameter of such an introducer is generally, however, on the order of only nine French. The consequence is that any device which is effectively insertable into the artery of a patient must be capable of assuming a configuration wherein the greatest dimension across the device is no more than approximately seven French. It happens, however, that to properly clear a stenotic segment it is sometimes necessary to create a lumen which has a greater diameter than seven French. To do this by an atherectomy procedure, the cutter being used must be capable of expanding beyond the seven French restriction imposed at the entry site.
Several examples of expandable cutting devices which are specifically useful as medical devices for atherectomy procedures can be given. U.S. Pat. No. 4,966,604 which issued to Reiss for an invention entitled "Expandable Atherectomy Cutter with Flexibly Bowed Blades", and U.S. Pat. No. 4,986,807 which issued to Farr for an invention entitled "Atherectomy Cutter with Radially Projecting Blade", both of which patents are assigned to the same assignee as the present invention, pertain to expandable atherectomy cutters. There is, of course, still a need for other expandable atherectomy cutters which can meet the specific needs of a specifically desired protocol.
The present invention recognizes that several factors need to be considered when determining the most desirable structure for an expandable atherectomy cutter and its method of use. First, there is the need to satisfy the personal preferences of the particular surgeon who is to perform the atherectomy operation. Clearly, different surgeons can have different approaches to the solution of the same problem. Further, there is the need to provide a structure which is best suited for performance of the particular task. It happens that atherectomy procedures can be performed in the coronary arteries, the carotid arteries, the renal arteries, and in the peripheral arteries. Each set of arteries is different and presents different challenges to the atherectomy procedure. The present invention provides such a structure for consideration and use by the operating physician.
In light of the above it is an object of the present invention to provide a compressible/expandable atherectomy cutter which can be reconfigured within an artery by manipulations performed externally of the patient. Another object of the present invention is to provide a compressible/expandable atherectomy cutter which can be configured into an operational rigid cutting configuration. Still another object of the present invention is to provide a compressible/expandable atherectomy cutter which is capable of making a reliable transition between a compressed configuration and an expanded configuration. Yet another object of the present invention is to provide a compressible/expandable atherectomy cutter which expands into a structurally predictable configuration. Another object of the present invention is to provide a compressible/expandable atherectomy cutter with is relatively simple to use, relatively easy to manufacture, and comparatively cost effective.